This project will investigate the interaction specificities of the estrogen receptor (ER) with DNA, reconstituted chromatin and isolated nuclei. It will determine what effect specific modulations of chromatin (e.g. bromodeoxyuridine-substitution of DNA, hyperacetylation of histones) have on the stability of ER-chromatin complexes. In a similar fashion, it will also determine how different estrogen and anti-estrogen ligands affect the affinity of ER for DNA, chromatin and nuclei. These experiments will employ a new kinetic procedure (Kallos et al., PNAS 75: 4896, 1978) which measures the rate of the receptor transfer from one DNA or chromatin fiber to another. This transfer procedure provides valuable information on the dynamic properties of the ER and may reflect the process by which ER locates its proper nuclear binding sites. In order to determine if altered binding of ER to chromatin is associated with altered expression of an estrogen-dependent gene product, we will determine the effect of specific chromatin modulations (BrdUrd-substitution, histone hyperacetylation) and of various estrogens and antiestrogens on the secretion of an estrogen-induced biological marker protein, gp 46, by cultured human breast cancer cells, MCF-7. In related phases of this project, we will investigate the specific interations of ER with histones, in the absence of DNA; and we will exploit the enhanced photochemical reactivity of BrdUrd-substituted DNA, to determine whether ER makes direct contact with DNA, and if so, whether it can be photochemically crosslinked to DNA, to reconstituted chromatin or to nuclei in situ.